Electric discharge tube



Sept. 22, 1931. A. BOUWERS ELECTRIC DISCHARGE TUBE Filed Oct. 6, 1925 Patented Sept. 22, 1931 UNITED- STATES. PATENT OFFICE 2 ALBERT :BOUWERS, F EINDHOV'EN, NETHERLANDS, ASSIGNOR TO N. V. PHILIPS 'GLOEILAIPENFABRIEKEN, 0F EINDHOVEN, NETHERLANDS ELECTRIC DISCHARGE TUBE Application filed October 6, 1925, Serial No. 60,891, and in the Netherlands January 28, 1925.

This invention relates to high-tension electric discharge tubes, and consists more particularly in an improved manner of protecting the seal of the envelope, which envelope :consists partly of a conductor and partly of a non-conductor.

In dischargetubes it often occurs that the inner wall of theenvelope is struck by charged particles which cause local charges to accu- 11: mulate thereon. Also conduction through the glass and along the surface of the glass may cause local charges. If high tensions are required to be supplied between the electrodes, as in the case of X-ray tubes and 1.; transmission tubes, these charges may cause disruption or cracking of the envelope wall and other undesired phenomena. Accordingly, it has heretofore frequently been proposed to partly shield the wall of the tube 2.} from being struck by charged particles, for example by electrons, by arranging screens 01 shields within the tube at some distance from the wall.

The above mentioned phenomenon is par- 1". ticularly inconvenient if the envelope of the discharge tube consists partly of a conductor and partly of a non-conductor, for example of glass, in which case the conducting and non-conducting parts are sealed to each other.

:1; This seal of the envelope is not efliciently capable of resisting high potential difference and therefore in arranging the said screens or shields attention has been paid principally to keeping the seal or seals as far as possible be- :15 yond the reach of the electrons.

This invention has for its object to provide another means for obviating the said inconvenience in a simple and effectual manner.

According to the present invention. the sur- 41) face of the discharge tube is provided with one or more conductive coatings which immediately cover the seal or seals. These coatings may consist, for example, of a strip of metal foil, such as lead foil or tin foil, disposed against the outer or inner surface of the'seal; or either the outer or the inner wall of the tube may be coated locally with a metal coating, for example, a silver mirror. In all cases the conductive coating should preferably be in contact on one side with the con- Frequently it may be advisable to have the it free end of the coating terminate in a rounded edge-rather than in a sharp edge in'order to reducethe field intensity attlie edge.

The device according to the invention is also adapted for use in combination with the 7 i i above mentioned screens or shields.

Theinvention will be more clearly understood with reference to the accompanying drawings in which Figure 1 represents an X-ray tu'be and Figure 2 represents atransmis'sion tu-be,the invention being applied to both tubes.

The X-ray tube represented in Figure '1, consists of a glass part 1 having scaled to it at 5 a metal'part '2, for example, of chromeiron to which is sealed at 4 a glass-window 3. The glass cylinder 1 has a re-entran-tpo'rtion to which is sealed at 6 a metal tube 7 carrying on the lower side an anticathode 8.

The electrons emitted by the incandescent g cathode .9, pass through a diaphragm 10 of a disc -11, and the rays emitted by the anticathode, can leave the tube through an aperture 12 of a disc 1'3an'dtl1r'ongh the window? Tothe tube 7 is secured a shield 14 which has consequently the same potential as the anticathode and which, together with a second shield 15 which is secured to the disc 11 and therefore has the same potential as the cathode, forms a kind of labyrinth packing whereby the passage of primary as well as secondary electrons is made difficult.

In order to'neutralize the harmful effect of the electrons which still penetrate, a conductive coatinglfi consisting, forexample of tin-foil, is arranged around the seal 5 which is the Weakest part of the tube. This coating 7 on one side is in contact with the metal wall 7 is not shown. i

The transmission tube represented in Figure 2 consists of a glass envelope 1 whlch has a rte-entrant portion 23, and which at 5 is ings.

sealed to a metal cylinder 2, forv example of chrome-iron,'which serves as anode and can be screwed intothe cover of a cooling'vessel, not shown. The re-entrant portion 23 of the vessel 1 ends in three glass tubes 24, 25 and 26 which are closed respectivelycby "metal discs 27,28 and 29, for example of chromeiron, and which servefor the supply of current to the incandescent grid. The current for the filament is supplied by flexible cables 21 and 33 and by wires the purpose of reducing the incathode and to the cludes a conductive and a non-conductive portion sealed together at their meeting edges, and means for protecting the seal from high potential disruptive forces comprising a conductive element which overlies the seal and extends along and in contact with the tube wall from a point on the conductive portion thereof that is beyond the seal.

3. In a hlgh-vacuum discharge tube operat ing substantially without ionization, thecom- V bination of an envelope wall which includes a conductive and a non-conductive portion sealed together at their meeting edges, and means for protecting the seal from high potential disruptive forces comprising a strip of metal foil which overlies the seal and extends along and in contact with the tube wall from a point on the conductive portion to a point on the non-conductive portion thereof that is beyond the seal.

In testimony whereof I aflix my signature, at the city of Eindhoven, this 16th day of September, A. 1)., 1925.

e V ALBERT BOUWERS.

20, 34: and 32, 35 which are secured on either side of the leading-in discs 27 and 29 respectively; The conductive connection with the grid is made by a rod 31 and a. wire 3O which are secured to both sides of the leading-in disc 28. I The rod 31fcarries a is woundthe grid wire not shown in the draw- Theseal-5 frame22 on which is protected by a strip 16 ofconductive' material, for example of tin-foil,

which is arranged around saidiseal on the outside and whereby in theinanner above de' scribed the danger to the seal 5 is averted and shiftedto the edge 17 of the protecting strip. This edge is not bent as it-is not absolutely necessary. It may however sired, as an extra measure of precaution.

. If desired, metal mirrors may besubstitut- The strips as well as the ed for the strips16. mirrors may be provided only on the inner surface of the seal or on the outer as well as on the inner surface.

What I claim is z 1." A high-tension discharge tube having an envelope which conslsts of a conductor hermet'ically sealed directly to a non-conductor and which is'pr'ovided with a device for pro-- tecting the seal from high potential disruptive forces, sai'l device consisting of at least one conductive coating which immediately covers be bent, if de- 'to a point on the non-conductive portion the seal and extends longitudinally of the tube envelope on both sides of the seal and is provided on at least one side of the surface f the envelope. 1

2. In a high-vacuum discharge tube operating substantially without ionization, the

combination of an envelope wall which in- 

